TSH levels: All you need to know

Thyroid-stimulating hormone (TSH) testing determines the level of TSH in the blood. The results show how well a person’s thyroid is working.

TSH test results can be used by doctors to diagnose thyroid problems such as hypothyroidism and hyperthyroidism.

TSH, a hormone that stimulates the thyroid gland, is produced by the pituitary gland.

The thyroid gland is a butterfly-shaped gland located in the throat. It secretes hormones that aid in the regulation of various biological systems, including metabolism, heart rate, and body temperature.

The TSH test and its findings are described in this article. We also go over what high and low TSH values mean and what therapies are available.

Typical TSH range

MNT-infographic_guide infographic by Diego Sabogal 1401179-TSH-levels-original
MNT-infographic_guide infographic by Diego Sabogal 1401179-TSH-levels-original

The typical range is determined by a person’s age and whether or not she is pregnant.

As a person gets older, the ranges tend to widen. TSH levels in males and females have not been found to differ consistently in studies.

However, doctors generally consider levels to be within a normal range of 0.4–4.0 milliunits per liter (mU/l), according to the American Thyroid Association.

TSH levels that are normal, low (showing hyperthyroidism), and high (indicating hypothyroidism) are estimated in the table below:

HyperthyroidismNormalMild hypothyroidismHypothyroidism
0–0.40.4–44–1010

These reference values are often used in laboratories.

These ranges, however, are subject to some disagreement. According to the author of a 2016 review, normal levels are more likely to be in the range of 0.5–2.5 milli-international units (mIU) per milliliter.

TSH levels by sex

Females are more likely than guys to suffer from thyroid problems. According to the Office of Women’s Health, one out of every eight females will encounter thyroid difficulties at some point in their lives. Hyperthyroidism and hypothyroidism are examples of this. Thyroid disorders are more common during pregnancy and around menopause.

TSH levels in males and females do not differ consistently, according to research. TSH levels are usually greater in females, according to some data. TSH levels are greater in females, according to 2020 studies of Chinese and French populations, although other factors, including as age, are more likely to alter TSH levels.

Thyroid problems have been connected to sexual dysfunction in certain people. Males may be affected more than females. According to a 2019 study, 59–63 percent of male hypothyroidism patients also suffer sexual dysfunction, compared to 22–46 percent of female hypothyroid patients.

TSH levels by age

Blood TSH levels tend to rise as people age, with research indicating that hypothyroidism is the most frequent thyroid condition in people over 60, and that it rises steadily with age.

According to research involving older persons, between 7–14 percent of people may have TSH levels over the upper limit of reference ranges.

Normal TSH levels in pregnancy

Pregnancy hormones naturally raise blood levels of some thyroid hormones. This is necessary for the unborn brain and nervous system to grow.

TSH levels in the blood decrease at the same time. As a result, during pregnancy, doctors adopt lower reference ranges. The lower TSH range is reduced by about 0.4 mU/l, while the higher limit is reduced by around 0.5 mU/l.

TSH levels in the blood steadily rise during the second and third trimesters, but they remain lower than in non-pregnant women.

TSH levels are carefully monitored by doctors throughout pregnancy. Having abnormally high or low levels might cause the risk of miscarriage and lead to pregnancy-related problems such as:

Normal TSH levels in children

TSH levels peak at birth and progressively decline as a child grows older. As a result, TSH levels can differ amongst children. After the newborn period, health professionals may describe moderate hypothyroidism in children as TSH levels ranging from 4.5 to 10 mU/l.

According to an older study that included data from 512 healthy children, the following table depicts TSH levels for children by age:

AgeReference ranges (mU/l)
Day of birth3.84–11.75
1 month1.18–3.57
1 year1.17–3.55
5 years1.15–3.47
12 years1.09–3.31
18 years1.05–3.16

What exactly do high levels imply?

TSH levels that are too high indicate hypothyroidism. When the thyroid produces insufficient hormones, people suffer hypothyroidism.

When a person’s thyroid gland does not generate enough hormones, the pituitary gland increases TSH production to compensate.

Hypothyroidism symptoms may include:

  • irregular or heavy menstrual periods
  • fertility problems
  • depression
  • constipation
  • fatigue
  • increased sensitivity to cold temperatures
  • dry skin
  • weight gain
  • swelling of the face and neck
  • thinning hair
  • a slow heart rate

What exactly do low levels imply?

TSH levels that are too low indicate hyperthyroidism. This is also referred to as an overactive thyroid.

When a person’s thyroid gland secretes high amounts of hormones, the pituitary gland generates less TSH.

Hyperthyroidism can cause the following symptoms:

  • difficulty sleeping
  • frequent bowel movements or diarrhea
  • weight loss
  • mood changes
  • irregular or rapid heartbeat
  • muscle weakness
  • nervousness or irritability

How to measure TSH levels

A healthcare practitioner will draw blood from a vein in the inner arm for the TSH test. They then submit the blood sample to a laboratory for analysis.

Typically, people do not need to prepare for a TSH test. If the doctor is screening the blood for more than one problem, the patient may need to fast or prepare in another way. This information will be provided by the doctor ahead of time.

A TSH test is frequently the most accurate approach to assess thyroid function. If a person’s TSH levels are excessively high or low, the doctor may need to run at least one further diagnostic test to determine the underlying cause. Specific thyroid hormones and antibodies are measured in these assays.

Factors influencing levels

TSH levels can be affected by a variety of circumstances, including age, sex, and pregnancy. TSH levels may be affected by genetic, environmental, or intrinsic causes, according to evidence. Some of these elements could be:

  • time of day and time of year
  • autoantibodies and heterophilic antibodies
  • smoking
  • pollutants
  • other conditions occurring at the same time
  • medications
  • supplements
  • ethnicity
  • diet and iodine status

Hypothyroidism treatment (high TSH levels)

Doctors can treat hypothyroidism with drugs that restore the missing thyroid hormones, such as levothyroxine.

This drug should be taken once a day or as directed. Every few months, the doctor will do further blood tests to see how well the medicine is working.

People should take levothyroxine once a day, on an empty stomach, at least half an hour before eating, according to the Food and Drug Administration (FDA).

The FDA also advises people to notify their doctor if they consume soybean flour, walnuts, dietary fiber, or cottonseed meal, as these foods can alter how the body uses levothyroxine. Drinking grapefruit juice may also delay levothyroxine absorption.

Treatment of hyperthyroidism (low TSH levels)

Treatment for hyperthyroidism focuses on lowering thyroid hormone levels in order to avoid long-term health consequences.

Beta-blockers and antithyroid medicines may be required.

Radioiodine therapy is another successful treatment. This entails ingesting a capsule or liquid containing radioactive iodine-131, which destroys thyroid hormone-producing cells. People who receive radioiodine therapy, on the other hand, may develop hypothyroidism in the future.

Severe hyperthyroidism can be treated surgically by removing the thyroid gland. Doctors frequently reserve this for patients who are unable to take first-line drugs or who have severe hyperthyroidism.

Conclusion

A TSH test determines the level of the hormone in the blood. The results can be used by doctors to diagnose thyroid problems such as hypothyroidism and hyperthyroidism.

Normal TSH readings can vary greatly based on age, sex, and weight. TSH reference ranges are still debatable, however for most people, the typical range is between 0.4 to 4.0 mU/l.

A thyroid that is overactive or underactive might cause health problems that interfere with a person’s daily life. TSH levels that are extremely high or low during pregnancy can cause difficulties.

More information about the TSH test and interpreting the findings can be obtained from a doctor.

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